FIG. 1 is a diagram illustrating control channels transmitted from a transmission apparatus. In the figure, the control channels are used in transmitting information necessary for performing reception, demodulation and decoding on a data channel i.e. control information including the number of multicodes, modulation scheme, the number of information bits, and so on. When there are a plurality of reception apparatuses, information indicating which reception apparatus the channel is for is coded and transmitted on each control channel, so that each reception apparatus is able to detect the control channel for the reception apparatus from among multiple received control channels.
FIG. 2 is a block diagram illustrating a configuration of a conventional reception apparatus. Reception apparatus 8 as shown in the figure is provided with antenna 9, duplexer 10, reception section 11, control channel reception section 12, control channel demodulation section 13, control channel decoding section 14, determination section 15, control section 16, data channel reception section 17, data channel demodulation section 18, data channel decoding section 19, error detection section 20 and transmission section 21. In such a configuration, signals of a plurality of (or a single) control channels are received in antenna 9, output to duplexer 10 and reception section 11 sequentially, and received in control channel reception section 12. The received signals of the plurality of control channels are input to control channel demodulation section 13, and subjected to demodulation for each channel. Each demodulation result is input to control channel decoding section 14. Control channel decoding section 14 performs decoding on the demodulation result of each of the plurality of control channels input from control channel demodulation section 13, and inputs the decoding results to determination section 15.
Based on each of the decoding results input from control channel decoding section 14, determination section 15 determines whether there is a channel intended for reception apparatus 8 among the received plurality of control channels. The determination is made, for example, using an error check bit and/or likelihood information calculated in control channel decoding section 14. When a control channel for reception apparatus 8 is present as a result of the determination, determination section 15 notifies control section 16 of the presence. Upon receiving the notification, control section 16 controls data channel reception section 17, data channel demodulation section 18, and data channel decoding section 19 to perform reception, demodulation and decoding on a data channel using control information indicated by the decoding result of the control channel for reception apparatus 8.
Meanwhile, error detection section 20 detects an error of decoded data input from data channel decoding section 19, and notifies control section 16 of the result. In the case of receiving the notification indicating that no error is detected from error detection section 20, control section 16 outputs an ACK (Acknowledgment) signal to transmit from transmission section 21. In the case of receiving the notification indicating that an error is detected from error detection section 20, control section 16 outputs a NACK (Negative Acknowledgment) signal to transmit from transmission section 21. Further, in the case where a control channel for reception apparatus 8 is not detected from a determination result in determination section 15, control section 16 does not perform reception of data channel.
In addition, a method is proposed that reception processing on a data channel is controlled using an error detecting code of control information added to the data channel in receiving the data channel (for example, Japanese Laid-Open Patent Publication 2000-244463).
However, conventional reception apparatus 8 as described above has such a problem that when the control channel determination misidentifies a control channel not for reception apparatus 8 as a control channel for reception apparatus 8, reception, demodulation and decoding on a data channel is carried out using wrong control information.
Further, when data channel signals are properly decoded accidentally using wrong control information, data to a reception apparatus except reception apparatus 8 is received, and there arise problems with inconsistency of data and confidentiality.
Furthermore, in a communication system using so-called hybrid ARQ (Automatic Repeat reQuest), when reception, demodulation and decoding on a data channel is once carried out using wrong control information, it is not possible to decode data accurately in error correction using subsequent retransmitted data, and gains in hybrid ARQ may be lost as a result.